This invention relates to covers, and, more particularly, to overcaps for pressurized or "aerosol" devices.
Aerosol containers typically have a cylindrical metal container body and a metal dome joined thereto by means of a circular doubleseam. An aerosol valve for dispensing the fluid contents of the container is typically mounted to the dome along the axis of the cylindrical metal container. It has been quite common to cover the domed end of an aerosol container and the dispensing valve attached thereto by means of a cover known as an overcap. Such overcaps typically snap over the doubleseam or over a snap bead which is normally formed in the dome somewhere near the cylindrical wall of the metal container body.
Such overcaps are typically made either of metal or, in some cases, of plastics such as polypropylene or high density polyethylene. Metal overcaps and plastic overcaps of the prior art have many significant disadvantages. Metal overcaps are often so rigid as to be quite difficult to remove them from engagement with an aerosol container. Furthermore, metal overcaps are known to be relatively expensive compared to overcaps made of plastic. Plastic overcaps, on the other hand, while being highly preferred from a cost standpoint, are often unacceptable for several other reasons.
Plastic overcaps, particularly overcaps for use on large-diameter aerosol containers (such as containers having diameters of 3.10 inches), are often susceptible to a retention problem in which the overcap is not firmly engaged with the aerosol container, allowing it to be easily dislodged. In some cases, while such plastic overcaps may be firmly engaged with the aerosol container in the initial capping, subsequent repetitive recapping during or between uses of the aerosol container will result in a breakdown in the attachment of overcap to aerosol container, making the attachment loose at best. This problem is often due to cold flow properties of the plastic materials used in such overcaps. Such cold flow characteristics may necessitate unreasonably tight dimensional tolerances in molding, which cannot be met in production. Tolerances which are achievable, on the other hand, have not consistently provided overcaps which may be attached firmly to aerosol containers.
This retention problem is exacerbated by top-loading forces which typically come to bear on the overcap, particularly during warehousing of finished aerosol products. Such excessive top-loading forces drive the overcap against the metal aerosol container thus tending to destroy the dimensioning which is essential to successful retention.